RC Beam Design Procedure

Reinforced Concrete Beam Design Procedure – Main Reinforcement

DATA State Effective Span of Beam – L (m)

Concrete Compressive Strength Class C?/?Characteristic compressive cylinder strength of concrete, fck (N/mm2)Characteristic strength of Reinforcement, fyk (500 N/mm2)Breadth of Beam – b (mm)Overall Depth of Beam – h (mm)Characteristic Loadings – Dead and Imposed (kN, kN/m, kN/m2)Main Bar – 16 - 40mmLink Bar – 8 - 12mm

DURABILITY & FIRE RESISTANCE State Exposure Class from T 4.1 (EC2) & Required Fire Resistance (mins)Determine Nominal Cover (mm) from T NA.2 (NA to EC 2) & T 5.2a (EC 2 Part 1-2)Calculate Effective Depth of Beam, d = h – cover – link½ main bar (mm)

LOADING @ ULSCalculate Design Ultimate Load, F = 1.35DL + 1.5 IL (kN) (=1.35×Gk + 1.5×Qk EC 0)

MOMENT @ ULSCalculate Design Ultimate Moment, MEd (=FL/8, =FL/4, =FL/6, etc) (kNm)

Calculate K = MEd/bd2fck (use N & mm)

Show that K < 0.167 (K’) State No compression steel required

Calculate Lever Arm Factorz/d = 0.5 + √( 0.25 – 0.882K )

Show that 0.82 ≤ z/d ≤ 0.95 State z/d OK

Calculate Lever Arm, z = z/d × d (mm)

MAIN REINFORCEMENTCalculate Required Area of steel reinforcement, As = MEd / 0.87fykz (mm2) (use N & mm)

Determine Number & of bars, such that Provided As > Required As

(e.g. Use 3H25 (1470mm2) )Show that As is between Max & Min Limits:

0.0013bd ≤ 0.00016 fck2/3bd ≤ As ≤ 0.04bh (mm2) State As OK

CRACKING @ SLS

Sketch A section through the beam showing the main bars, links, clear & bar spacing.

Show that Clear spacing is greater than minimum limits = 25mm, or max bar

Calculate Service stress, s & hence the max bar & spacing from T 5.6 (ISE Manual)

Show that Bar diameter OR bar spacing is less than the maximum values from T5.6 State Cracking OK

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RC Beam Design Procedure

Reinforced Concrete Beam Design Procedure – Shear Reinforcement

SHEAR @ ULSDetermine Design value of the applied Shear Force, VEd (kN)

= Max SF from SFD, at the support for a SSB

Calculate Design Shear Stress, vEd = VEd/bw0.9 d (N/mm2) State bW

CONCRETE STRUT CHECKDetermine Capacity of Concrete Struts, vRd,max (N/mm2)

from Table 7.2 (Concise EC2), for o and fck

For beams with low shear stress: = 21.8o, look up vRd,max value in bold column:Show that vEd < vRd,max

State that cot= 2.5 State OK against crushing Go to Shear Reinforcement

For beams with high shear stress: 21.8o < < 45, look up vRd,max value in other column:

Show that vEd < vRd,max

Calculate = 0.5 sin-1[vEd /0.20 fck(1 - fck/250)] Calculate cot

Show that cot>1.0 State OK against crushing Go to Shear Reinforcement

SHEAR REINFORCEMENT For beams with low shear stress

Calculate vEd bw/1087 (mm2/mm)

Assume Asw/s (mm2/mm) Refer to Rebar Ratio Tables

Asw = Area of Shear Steel, in mm2, & Link Spacing = s, where max s = 0.75d mm,

Show that Asw/s ≥ vEd bw /1087 (mm2/mm) Go to Shear Reinforcement Checks

For beams with high shear stressCalculate vEd bw/435cot

Assume Asw/s (mm2/mm) Refer to Rebar Ratio Tables

Asw = Area of Shear Steel, in mm2, & Link Spacing = s, where max s = 0.75d mm,

Show that Asw/s ≥ vEd bw /435cot(mm2/mm) Go to Shear Reinforcement Checks

SHEAR REINFORCEMENT CHECKSCalculate 0.08 fck

0.5 bw /500 (mm2/mm) Minimum value

Show that Asw/s ≥ 0.08 fck0.5bw /500 (mm2/mm) State Asw/s OK

Show that 75 < s < 0.75d (mm) State Link Spacing OK

State Bar Type, ,and Spacing of Links eg H8 @ 200c/c (H8-03-200)

Reinforced Concrete Beam Design Procedure– Deflection Check

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RC Beam Design Procedure

DEFLECTION @ SLSCalculate Actual span-to-effective-depth ratio, L/d

Calculate Required tension reinforcement ratio, = (As,req /bd)×100 ( % )

Determine Basic span-to-effective-depth ratio, N from Table 15.10. (Concise EC2), for and fck

Determine Factor K from Table 15.11. (Concise EC2), for beam type

Calculate beff/bw beff = bw for rectangular sections

Determine Factor F1 from Table 15.12. (Concise EC2), for flanged beam geometry.

State that Factor F2 = 1 for non brittle partitions over a 7m+ span

State Service stress, s = 435×(Gk + 0.3Qk /1.35×Gk + 1.5×Qk)×(As req /As prov) (N/mm2)

As req is the area of tension reinforcement required at the section considered for the ultimate limit state.

As prov is the area of reinforcement actually provided.

Calculate Factor F3 to account for service stress in tensile reinforcement = 310/s ≤ 1.5

Calculate Allowable L/d= N x K x F1 x F2 x F3

Show that Actual L/d ≤ Allowable L/d State Deflection OK

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